Why does this script cause problems only on Jenkins? - jenkins

Question

I had to add a job in a multibranch pipeline.
The goal was to automatically install a plugin in jira.
The code runs perfectly fine because I tested it in a Unit Test.
But when I put it as a scripted pipeline on Jenkins, it does not do what it should do.
The goal is to install the plugin on jira, but when I run it on Jenkins it will not be installed.
Also I do not get any json Response, which I get in my JUnit Test.
I really do not know what is different on Jenkins. I already found it weird that I have to approve every single method in my script. Did someone have a similar issue on jenkins before.
I really appreciate your help.
#Test
public void test_install_plugin() throws IOException {
String jsonBody = "{\"pluginUri\": \"http://myServer/job/element/job/mybranch\", \"pluginName\": \"myPlugin\"}";
String token = "-6485649001990379871";
String jiraPath="myServer/rest/plugins/1.0/";
String query = "token="+token;
String url = jiraPath+"?"+query;
URL jiraURL = new URL(url);
HttpURLConnection jiraURLConnection = (HttpURLConnection)jiraURL.openConnection();
jiraURLConnection.setDoOutput(true);
jiraURLConnection.setDoInput(true);
jiraURLConnection.setRequestProperty ("Content-Length",String.valueOf(jsonBody.length()));
jiraURLConnection.setRequestProperty ("Accept", "application/json");
jiraURLConnection.setRequestProperty ("Content-Type", "application/vnd.atl.plugins.install.uri+json");
jiraURLConnection.setRequestProperty ("Authorization", "Basic YWRXXXXXXtaW4=");
jiraURLConnection.setRequestMethod("POST");
OutputStream os = null;
try {
os = jiraURLConnection.getOutputStream();
byte[] input = jsonBody.getBytes("utf-8");
os.write(input, 0, input.length);
os.flush();
}
catch(IOException ex)
{
System.out.println("Exception: " + ex.getMessage());
}
finally
{
os.close();
System.out.println("responseCode of install request: " + jiraURLConnection.getResponseCode());
}
BufferedReader br = null;
try {
br = new BufferedReader(new InputStreamReader(jiraURLConnection.getInputStream(), "utf-8"));
StringBuilder response = new StringBuilder();
String responseLine = null;
while ((responseLine = br.readLine()) != null) {
response.append(responseLine.trim());
}
System.out.println("Response: " + response.toString());
}
catch(IOException ex)
{
System.out.println("Exception: " + ex.getMessage());
}
finally
{
br.close();
jiraURLConnection.disconnect();
}
}